Method of handling pigments for heat treatment



Oct. 16, 1934. M HANAHAN METHOD 0F HANDLING PIGMENTS FOR HEAT TREATMENTFiled April 22. 1951 Mario/z L. Hama/zam A mm1, BMQWAW.

BY ATTORNEYS Patented ct. I6, 1934 UNIT? 'ST- "Marion L. IIa

TES PATENrf- OFFICE 1,977,582 .l 4 l Y i i'v'ra'rnon oF HANDLINGPIGMN'rs HEAT TREATMENT nahan, East Orange, N. li., assgnor,

FOR Q by mesne assignments, to Krebs Pigment it` Color Corporation,Wilmington,

tion of Delaware Del., a corpora- I Application April 22, 1931,Serial-No. 531,945

7 Claims.

This .invention relates to a. particular method of handling pigments soas to subject them to the action of high temperatures and pressures inthe presence of moisture, and. may be considered 5 as a particular formof and method of utilizing the invention broadlydisclosed in theco-pending application of Chester C. Feagley, Serial No. 532,135 led oneven date herewith. 'Ihe present .application contains matter derivedfrom and is in part a continuation of my earlier application, Serial No.409,294, filed November 23, 1929.

According to my process, the pigment, in a finely divided state, iscombined with water to form a slurry, or liquid suspension, and is thenforced substantially continuously through a heated zone while thepressure is maintained high enough to permit the` continuousintroduction of material to betreated, against the back pressure. Anappropriate valve is maintained at the discharge end of the systemthrough which the treated material is permitted to pass at approximatelythe same rate as it is introduced at the feed end.

. Various forms of apparatus may be used for heat treating thematerialas, for example, the slurry may be passed continuously through coilswhich are heated externally, ormay be passed into an autoclave soarranged that as new material is introduced into the autoclave, thetreated material will be ejected therefrom. For the purpose of economyit is highly desirable to arrange for -a heat exchanger so that thematerial which has ,been subjected to high temperatures may give up alarge lpart of its heat to material that is being introduced into theapparatus. Itis also advisable to maintain a pressure regulating deviceconnectedwith the system so that a substantially constant pressure andflow of material v may be maintained.

The temperatures used in the heated zone may vary over a wide range, -asfor example, from between 200 C.,to in the `order of 700 C., though.

if the critical point of water is passed, particular means-may have tobe employed to maintain the pigment in motion so that asthe temperaturedrops, the water will condense to re-establish the slurry; otherwise,stoppages may occur. For this reason, I find it more practical to keepthe tem-U perature below the critical point of water (375 C.) I also ndthat at temperatures as low as 200 C. the eiect-is unduly slow andaccordingly I find it advantageous to operate at temperatures above250C. and preferably above 300 C.

The pressuremay 'be just enough above the pressure of saturated steam atthe given subcritical temperatures (or when working above the criticaltemperature, it should be above the critical pressure), so that thematerial is fed forward constantly, but higher pressures may be usedwithout injury, though there apparently is no particular advantage inusing such high pressures and they simply add to the cost of equipment.Thus the pressures used may vary from about 215 pounds gauge pressure upto in excess of 6,000 pounds. The time of treatment will vary with thetemperature and may range from 5 or 10 minutes upto several hours.

I nd that by operating in this manner and maintaining the temperaturesand pressures so adjusted that substantially all the moisture remains inthe liquid phase, that the process can be conducted continuously atrelatively low cost and with great efficiency.

`For the purposes of illustration, I show in the accompanying drawing,an apparatus that may be used for carrying out my process. In thedrawing, 2 is a storage tank for the pigment mixed with water to form aslurry. This slurry is withdrawn from tank 2 by pump 4 which forces thematerial under pressure through pipe 6, provided with check valve 7,into the heat exchanger 8. Preferably connected to the pipe 6 is apressure reservoir 10 wherein the pressure is maintained substantiallyconstant while permitting limited variations in volume, as by havingthis reservoir connected by pipe 12 with any desired source of highpressure inert gas, such as nitrogen. If preferred, a hydraulicaccumulator may be used with approximately equal results.

It is to be understood that heat exchanger 8 is provided with the usualcoils which are not here shown, but the connections between the two pipesystems are indicated by dot and dash lines. After passing. through thecoils of the heat exchanger, the warmed up slurry passes through Apipe14 into the heating coils indicated at 16. These coils are heatedexternally in any desired way as by an appropriate form of vapor such asmercury vapor or the vapor of diphenyl, which is supplied from a heater18 through a pipe 20 and returns through a pipe as indicated at 22. Theslurry which has been brought up to the desired temperature in theheating coils 16 passes into the jacketed autoclave 24 which is likewiseheated as by vapor from heater 18 (or inlany other desired manner), thesupply line for the vapor being indicated diagrammatically at 26 and thereturn at 28. The autoclave 24 is supplied with appropriate stirringmechanism which may be driven by a motor 30.

` After the slurry has passed slowly through the autoclave 24, it comesout through pipe 32 and is returned to the'heat exchanger 8 and nally isdischarged through pipe `3,4 which is provided'with appropriate valve36. A receptacle for the nnished product is indicated at 38. Valve 36(which may be either a hand-operated valve or anv automaticl pressurerelease valve) must beset torestrict the discharge oriiice to maintainthe desired pressure in the system, and the pump 4 must have sufficientpower to force the slurry through the system against the back pressurecreated by the partial closing of v'alve 36 and also to maintain theamount of water and pressure suicient so that while the temperature isbelow the critical,A

Yslurry in the formof steam, the slurry will expand and contractsubstantially as a homogeneous mixture and the relative masses of thesolid material and water are maintained substantially constantthroughout the pressure system. Apparently it is the relative mass ofsurrounding water which is important, and my invention not only permitsme to make the process continuous, but also gives a ready method ofmaintaining the mass ratio substantially constant over a wide range oftemperatures and of maintaining ,this mass ratio proportional to a massratio of sub-,r divided solid particles suspended in water, even Y afterthe critical temperature has been passed,

thereby aiding in standardization of results. In the present case, thisis primarily made possible by the fact that'the pressure lis maintainedsubstantially `constant while permitting the slurry to expand under theinfluence of heat, rather than having the pressure a function of thetemperature.

cessfully using less than one part of water with one part of pigment,though ordinarily I find that the material is easier to handle ifsomewhat more water is employed.

The maintenance of the mass ratio between the water and pigment not onlyaffects the process, but is also of Very considerable value in obtainingheat efiiciency for all the heat given to the slurry may be returnedv tothe heat exchanger except such'losses as occur through radiation. Inthisconnection, it is of course to be understood that the pipes and variousitems of equipment will be properly insulated to conserve heat, and itis also to be understood that the autoclave 24 and heater coils 16 maybe heated in any desired fashion asfor example by gas, or electricalresistance elements.

Instead of cooling the autoclaved slurry to a point where it will remainliquid after having passed the relief valve, I may dispense with thecooling, and/or part of the heat exchange and.

locate the relief valve at a point of the system where the slurry has atemperature substantially above 100 C. The relief valve should then lead.into a collecting chamber and the water of the slurry will beimmediately evaporated and thepigment settle out in the chamber in solidand dry form.

As regards the mass ratio used, I have 'found that the process can beoperated suc- This process may be applied to any pigment where-it isdesired to subject the same to the combined action of heat and pressurein the presence of moisture, and I have found that it is particularlyuseful in the treatment of lithopone or other pigments comprisingzincvsulphide, but I do not intend to limit its use to this particularclass of pigments, though in this case there appear to be indicationsthat some advantageous results are obtained by maintaining the pigmentactually in the form of a liquid suspension during the heat treatment.With zinc sulphide pigments, the best results that I have obtained havebeen where the precipitated material is prepared in the manner set forthin my co-pending application, Serial No. 531,946, filed Apr. 22, 1931.

While this lprocess has been `discussed in connection with the use ofwater as the liquid medium, it is my belief that more or less valuableresults can be obtained usingother liquids, particularly if smallamounts of water are present such as ordinarily will be held byadsorption or present as water of hydration. I should expect that themost satisfactory results would be obtained using liquids having arelatively high criti- 'cal temperature particularly liquids in whichthe pigment may be very slightly soluble. Accordingly, I believe thatthe most probable liquids to substitute for waterl are relatively highboiling liquids having a hydroxyl group, suchk as glycerine or otheralcohol or phenol, though it may be possible to use rather low boilingmaterials such as ammonia. These or other soluble substances may ifdesired be included with water.

What I claim is:

1. vThe process of treating pigments which comprises forming aslurrycomprising a subdivided pigment and water and heating such slurry toatemperature ranging upward from ,200 C. while maintaining the pressureand amount of Water in the slurry suilicient, when the temperature isbelow the critical temperature of water, substantially to illl withwater in the liquid phase the space not occupied by solids.

2. The process of treating pigments which com- 1 prises forming a slurrycomprising a subdivided pigment and a liquid and heating such slurry toa temperature ranging upward from 200 C. while maintaining the pressureand amount 4of liquid in the slurry sumcient, whenkthe temperature is 1below the critical temperature of such liquid, substantiallyto till withsuch liquid in the liquid phase the space not occupied by solids.

3. 'The process of treating pigments which comprises forming a slurry ofa subdivided pigment 1 and wa`ter and heating such slurry to atemperature ranging between 200 C. and the critical temperature ofwater, while maintaining the pressure and amount of water great enoughsubstantially to keep the water in the liquid phasel of water,substantially to fill with water in the liquid phase the space notoccupied by solids.

5. The process of treating pigments which comprises forming a slurrycomprising a pigment ,and water, forcing such slurry through a pressuresystem having a restricted oriiice, heating the 1 in such slurrysubstantially constant.

7. In the process of treating pigments, the step `oi.' treating asuspension of a pigment in a liquid at a temperature substantially abovethe normal boiling point of such liquid, while maintaining the pressureabove the pressure of a saturated vapor 'of such liquid at suchtemperature, whereby taining the relative masses of the water andsolids.

vaporization of thelliquid is substantially prevented. Y.

. MARIONv L. HANAHAN.

